The present invention relates to a magnetoresistive element, a device utilizing a magnetoresistance effect, and a magnetic sensor utilizing a magnetoresistance effect for reading information signals recorded in a magnetic recording medium, and more particularly to a tunnel junction device having an improved flat non-magnetic layer.
Magnetoresistive sensor and magnetoresistive head have been known as transducers for sensing a magnetic signal and transforming the same into an electrical signal. The magnetoresistive sensor performs to read data from a surface of a magnetic medium at a large linear density. The magnetoresistive sensor has a magnetoresistive element utilizing a magnetoresistance effect for sensing an intensity and a direction of a magnetic flux and transforming variations in intensity and direction of the magnetic flux into a variation in electrical resistance, so as to detect magnetic field signals, wherein one component or one directional component of the resistance varies in proportional to a square of a cosine of an angle defined between a magnetization direction of the magnetoresistive element and a direction along which a sensing current flows through the magnetoresistive element. This effect of such the variations in resistance of the magnetoresistive element is so called as an anisotropic magnetoresistance effect.
More detailed descriptions for the anisotropic magnetoresistance effect are described in IEEE Trans. On Mag. MAG-11, P. 1039 (1975) entitled xe2x80x9cmemory, storage, and related applicationsxe2x80x9d. In general, the transducer, for example, the magnetic head utilizing the anisotropic magnetoresistance effect is applied with a longitudinal bias for suppressing Barkhausen noises. In order to apply the longitudinal bias, anti-ferromagnetic materials such as FeMn, NiMn and nickel oxide are used.
Recently, it also has been known that the variation in resistance of a lamination-structured magnetic sensor causes a more remarkable magnetic resistance effect. This magnetoresistance effect is derived from a spin-dependent transmission of conductive electrons between magnetic layers sandwiching a non-magnetic layer and a spin-dependent scattering which incidentally appears to the spin-dependent transmission on an interface of the lamination-structured magnetic sensor.
Those magnetoresistance effects are different from the anisotropic magnetoresistance effects and are so called as xe2x80x9cgiant magnetoresistance effectxe2x80x9d or xe2x80x9cspin valve effectxe2x80x9d. The magnetoresistive element utilizing the giant magnetoresistance effect or spin valve effect derived from the spin-dependent scattering and the spin-dependent transmission shows a larger variation in resistance than and is more improved in sensitivity than the above described sensor utilizing the anisotropic magnetoresistance effect. The magnetoresistive sensor utilizing the giant magnetoresistance effect or spin valve effect shows a variation in sheet resistance or in-plane resistance between paired ferromagnetic layers sandwiching a non-magnetic layer, wherein the variation is proportional to a cosine of an angle between two magnetization directions of the paired ferromagnetic layers.
In Japanese laid-open patent publication No. 2-61572, it is disclosed that a magnetic layered structure exhibits a large variation in magnetoresistance caused by an anti-parallel order of magnetization in the magnetic layer. It is also disclosed that ferromagnetic transition metals and ferromagnetic alloys are available for the above layered structure. It is further disclosed that one of the two ferromagnetic layers sandwiching the non-magnetic layer is added with a pinned layers and FeMn is available for the pinned layer.
In Japanese laid-open patent publication No. 4-358310, it is disclosed that a magnetoresistive sensor has two ferromagnetic thin layers separated by a non-magnetic metal thin layer, wherein under no application of a magnetic field, individual magnetization directions of the two ferromagnetic layers are perpendicular to each other. A resistance between the separated two ferromagnetic layers varies in proportional to a cosine of an angle defined between the individual magnetization directions of the two ferromagnetic layers, but independently form a direction of a current flowing through the sensor.
In Japanese laid-open patent publication No 4-103014, it is disclosed that a ferromagnetic tunnel junction device has a multi-layered ferromagnetic structure having an inserted intermediate layer. This ferromagnetic tunnel junction device is characterized in that at least one of ferromagnetic layers is applied with a bias, magnetic field from an anti-ferromagnetic layer.
In Japan applied magnetic conference 1996, p. 135, it is disclosed that the tunnel junction device has a free magnetic layer of Co and a pinned magnetic layer NiFe.
In Japanese laid-open patent publication No. 10-65232, it is disclosed that one or two of Ni, Pd, Hf are added to Co-based magnetic alloy for ferromagnetic layers.
In Japanese laid-open patent publication No. 10-135038, it is disclosed that CoZrNb, CoZrMo, FeCoNb are available for the free magnetic layer.
In order to realize a stable property of variation in magnetoresistance of the tunnel junction device, it is important that the non-magnetic layer is so flat as possible, because if the non-magnetic layer is not flat, then variation in thickness of the non-magnetic layer causes a leakage of current which causes reduction in rate of variation in resistance. This leakage of current also causes breaking a thinner portion of the non-magnetic layer. This means that the leakage of current deteriorates the withstand voltage characteristic of the tunnel junction device.
The conventional tunnel junction device uses Co or NiFe for the free magnetic layer and the pinned magnetic layer. However, those materials are crystal, for which reason a most surface of each of the free magnetic layer and the pinned magnetic layer has a roughness which corresponds to the crystal structure. If, for example, the tunnel junction device has a multi-layer structure of xe2x80x9cfree magnetic layer/non-magnetic non-conductive layer/pinned magnetic layer/pinning layerxe2x80x9d and if the free magnetic layer is made of the above material, an interface roughness between the free magnetic layer and the non-magnetic layer makes it difficult to form a sufficiently flat non-magnetic layer, thereby causing drops in rate of the variation in resistance and also the withstand voltage characteristic. Also if the tunnel junction device has a multi-layer structure of xe2x80x9cpinning layer/pinned magnetic layer/non-magnetic non-conductive layer/free magnetic layerxe2x80x9d and if the pinned magnetic layer is made of the above material, an interface roughness between the free magnetic layer and the non-magnetic layer makes it difficult to form a sufficiently flat non-magnetic layer, thereby causing drops in rate of the variation in resistance and also the withstand voltage characteristic.
In the above circumstances, it had been required to develop a novel magnetoresistive element free from the above problem.
Accordingly, it is an object of the present invention to provide a novel magnetoresistive element free from the above problems.
It is a further object of the present invention to provide a novel magnetoresistive element having a highly flat non-magnetic layer.
It is a still further object of the present invention to provide a novel magnetoresistive element exhibiting a high rate of variation in resistance.
It is yet a further object of the present invention to provide a novel magnetoresistive element having an improved withstand voltage characteristic.
The third present invention provides a magnetoresistive device including a multi-layered structure of a free magnetic layer, a non-magnetic non-conductive layer in contact with the free magnetic layer, a pinned layer in contact with the non-magnetic non-conductive layer, and a pinning layer in contact with the pinned layer for pinning a magnetization direction of the pinned layer, wherein at least any one of the free magnetic layer and the pinned layer has an interface region abutting the non-magnetic non-conductive layer, and at least a part of the interface region includes at least one material selected from the group consisting of CoFeB, CoZrMo, CoZrNb, CoZr, CoZrTa, CoHf, CoTa, CoTaHf, CoFeTi, CoNbHf, CoHfPd, CoTaZrNb, and CoZrMoNi. Those materials are amorphous or fine crystal with fine crystal grains, for which reason the non-magnetic non-conductive layer is highly uniform in thickness and extremely small in surface roughness. The non-magnetic non-conductive layer is also highly flat and extremely small in surface roughness, whereby a magnetoresistance rate is improved high and a withstand voltage characteristic is also improved.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.